The present invention relates to clutches, and more particularly to viscous clutches.
Viscous clutches are used in a wide variety of automotive applications, such as to drive fans, pumps and the like, as well as in other contexts. These clutches typically employ relatively thick silicone oil (generally called shear fluid or viscous fluid) for the selective transmission of torque between two rotatable components. It is possible to engage or disengage the clutch by selectively allowing the oil into and out of a working area of the clutch located between input and output members. In a typical viscous clutch, the rotational input is a rotor disk connected to a drive shaft or pulley, and the rotational output is a housing or cover that can be connected to a fan, pump, shaft or other output element. A valve is used to control the flow of the oil through the working area between the input and the output. It has become common for the clutch to be controlled electrically. This has been done to increase the controllability of the clutch, and to also have the clutch capable of responding to multiple cooling needs in a vehicle, such as to respond to coolant temperature, intake air temperature, air conditioning pressure, and/or oil temperature.
Viscous clutches have been used in the past as a separate device installed on a rotating pulley on the engine front. Rotational inputs to the clutch have been traditionally been engine crankshafts and water pumps. During the past decade, cooling requirements have been increasing as a result of increasingly stringent engine emission reduction requirements. During this time, the use of a belted pulley has become a more common method of providing an input to the fan clutch, with the belted pulley (synonymously called a sheave) capable of increasing the fan speed in order to obtain more cooling air flow for a vehicle's heat exchanger(s). The belted drive is desirable due to its simplicity, low cost and ease of obtaining desired rotational speed. Due to the rotational input to the fan clutch being separated from the water pump or crankshaft, it is possible for the cooling system engineer to choose the exact fan speed required to provide the necessary and desired cooling for a given application.
Examples of viscous clutches include those disclosed in commonly-assigned U.S. Pat. No. 7,938,240 and PCT Published Applications WO 2011/062856A3 and WO 2012/024497A3. Further examples of viscous clutches include those disclosed in U.S. Pat. Nos. 4,046,239; 6,419,064 and 7,828,529, in U.S. Published Pat. App. No. 2012/0164002, and in European Published Patent Application No. EP 2 487 380 A1.
It is therefore desired to provide an alternative clutch design that is suitable for use with relatively high input speeds and torque loads, has relatively low mass, and provides relatively good heat dissipation, among other possible features and benefits. In addition, or in the alternative, it is desired to provide an alternative clutch design that is adaptable to a variety of applications without the need for extensive customization and whole-clutch re-design, among other possible features and benefits.